1. Field of the Invention
The present invention relates to an axis determination apparatus, a film-thickness measurement apparatus, a deposition apparatus, an axis determination method, and a film-thickness measurement method. More particularly, the present invention relates to an improvement of a technique that enables the determination of a film-thickness distribution by measuring the thickness of an electrically conductive film, at a plurality of points thereon, the film being deposited on a surface of a circular wafer.
2. Description of the Related Art
In many cases, it is customary to use generally circular wafers for the fabrication of semiconductor devices.
A wafer, designated by 150 in FIGS. 32(a) and (b), has a thin film deposited on a surface thereof. FIG. 32(b) is a cross-sectional view taken along line Xxe2x80x94X of FIG. 32(a). The wafer 150, formed of silicon, having a circular shape, is provided with an electrically conductive thin film 152 deposited on a surface of a substrate 151, on part of the circumferential portion of which there is formed a triangular cut-away portion (hereinafter referred to as the notch) 153.
In order to determine whether the thin film 152 has been deposited in a constant thickness on the surface of the substrate 151, it is necessary to measure the thickness of the thin film 152 at a plurality of points on the surface of the wafer 150 to thereby determine the film-thickness distribution and know the extent of variations in the film thickness measured at each point.
Now, referring to FIGS. 33(a) and (b), a step height method as one of a prior-art method for determining a film-thickness distribution is described below. FIG. 33(b) is a cross-sectional view taken along Yxe2x80x94Y of FIG. 33(a). In the step height method, the thin film 152 is deposited on the surface of the wafer 150, which is then taken out of the deposition apparatus. Subsequently, the thin film 152 is etched at predetermined positions on the surface of the wafer 150 (i.e., at the center of the wafer 150 and at both ends of center axis lines of the surface of the wafer). A plurality of openings 1561-1565 are thus formed to expose the surface of the substrate 151, as shown in FIG. 33(a). Thereafter, a stylus 171 is drawn near each of the openings 1561-1565 to measure the step height between each of the openings 1561-1565 and the electrically conductive thin film on a portion other than on the openings 1561-1565, thereby determining the thickness of the thin film near each of the openings 1561-1565 and the film-thickness distribution.
In the step height method, it is necessary to take the wafer 150 once out of the deposition apparatus to etch the aforementioned predetermined position and thereby form an opening, and thereafter draw the measurement stylus near the opening. Accordingly, there existed a problem of making the process considerably complicated.
The present invention was developed to solve the aforementioned drawbacks of the prior art. It is therefore an object of the present invention to provide a technique, which enables the accurate determination of the center axis of a circular substrate in a short time and the precise determination of the film-thickness distribution of a thin film deposited on the substrate surface.
To solve the aforementioned problems, the present invention provides an axis determination apparatus for determining a center axis line of a surface of a circular substrate. The axis determination apparatus comprises a support mount for supporting the substrate placed on a surface thereof, a drive mechanism for rotating the support mount in a plane containing the surface of the support mount, a light-emitting device disposed near the circumferential portion of the support mount, and a light-receiving device disposed, opposite to the light-emitting device, near the circumferential portion of the support mount. The light-emitting device is adapted to emit a beam of light to the light-receiving device.
The axis determination apparatus according to the present invention is such that the light-receiving device is disposed so as to receive the beam of light emitted by the light-emitting device through a notch provided on the circumferential portion of the substrate when the notch stays between the light-emitting device and the light-receiving device.
The present invention also provides an axis determination apparatus, for determining a center axis line of a surface of a circular substrate, comprising a support mount for supporting the substrate placed on a surface thereof. The axis determination apparatus further comprises a lifter, including a support member formed generally in a shape of a cube arranged on a circumference with a center of the support mount and a projected member projected towards the center under the support member, for supporting the substrate with a circumferential portion of the substrate sitting on the projected member. The axis determination apparatus further comprises a lifting mechanism for hoisting and lowering the lifter near the support mount. The axis determination apparatus is such that the support member is provided with an inclined surface sloped towards the projected member, and the lifter, when lowered below the support mount while supporting the substrate, transfers the substrate onto the surface of the support mount.
Furthermore, the axis determination apparatus according to the present invention is such that the substrate is clamped against the support mount.
Furthermore, the present invention provides a film-thickness measurement apparatus comprising an axis determination apparatus for determining a center axis line of a surface of a circular substrate and a measurement apparatus for measuring a thickness of an electrically conductive thin film formed on the surface of the substrate. The axis determination apparatus includes a support mount for supporting the substrate placed on a surface thereof, a drive mechanism for rotating the support mount in a plane containing the surface of the support mount, a light-emitting device disposed near a circumferential portion of the support mount, and a light-receiving device disposed, opposite to the light-emitting device, near the circumferential portion of the support mount, the light-emitting device being designed to emit a beam of light to the light-receiving device. The measurement apparatus determines a measurement position on the surface of the substrate at the measurement position in accordance with the center axis line determined by the axis determination apparatus and measures the thickness of the electrically conductive thin film at the measurement position.
Furthermore, the film-thickness measurement apparatus of the present invention is such that the measurement apparatus comprises a film-thickness sensor, a power source, and a measurement device. The film-thickness sensor includes a measurement coil. The power source applies an AC voltage to the measurement coil when the substrate is in close proximity to the measurement coil to generate an eddy current in the electrically conductive thin film on the surface of the substrate. The measurement device is designed to measure a signal generated in the measurement coil by an effect of the eddy current.
Furthermore, the film-thickness measurement apparatus according to the present invention is such that the film-thickness sensor comprises a reference coil and two reference resistors. The reference coil is connected in series to the measurement coil and arranged to stay farther away from the substrate than the measurement coil when the measurement coil faces the substrate. The two reference resistors are connected in series to each other to form a serially-connected circuit, which is connected in parallel to the serially-connected circuit of the measurement coil and the reference coil. The measurement device is designed to measure the potential difference between the connection of the measurement coil and the reference coil and the connection of the two reference resistors as a signal generated in the measurement coil when an AC voltage is applied across the serially-connected circuit of the measurement coil and the reference coil.
The present invention also provides a deposition apparatus comprising deposition means for depositing a thin film on a surface of a circular substrate and a film-thickness measurement apparatus for measuring a thickness of the thin film on the surface of the substrate. The film-thickness measurement apparatus includes an axis determination apparatus for determining a center axis line of the surface of the circular substrate and a measurement apparatus for measuring the thickness of an electrically conductive thin film formed on the surface of the substrate. The axis determination apparatus includes a support mount for supporting the substrate placed on a surface thereof, a drive mechanism for rotating the support mount in a plane containing the surface of the support mount, a light-emitting device disposed near a circumferential portion of the support mount, and a light-receiving device disposed, opposite to the light-emitting device, near the circumferential portion of the support mount, the light-emitting device being designed to emit a beam of light to the light-receiving device. The measurement apparatus determines a measurement position on the surface of the substrate at the measurement position in accordance with the center axis line determined by the axis determination apparatus and measures the thickness of the electrically conductive thin film at the measurement position.
The present invention further provides an axis determination method for determining a center axis line of a surface of a circular substrate having a notch on part of a circumferential portion of the substrate. The method comprises the steps of determining a center of the surface of the substrate, and irradiating the circumferential portion of the substrate with a beam of light emitted from a light-emitting device. The irradiation is carried out while the substrate is being rotated in a plane containing the surface of the substrate with the center of the surface. At this time, the light-emitting device stays opposite to a light-receiving device to interpose the circumferential portion of the substrate therebetween. The position of the notch is thus detected depending on whether or not the beam of light passes through the notch to be received by the light-receiving device. The method further comprises the step of determining the center axis line of the surface of the substrate in accordance with the position of the notch and the center of the surface.
The present invention further provides a film-thickness measurement method, comprising the step of determining a center of a surface of a circular substrate having a notch formed on part of a circumferential portion of the substrate and having an electrically conductive thin film deposited on the surface. The method further comprises the step of irradiating the circumferential portion of the substrate with a beam of light emitted from a light-emitting device. The irradiation is carried out while the substrate is being rotated in a plane containing the surface of the substrate about the center of the surface. At this time, the light-emitting device stays opposite to a light-receiving device to interpose the circumferential portion of the substrate therebetween. The position of the notch is thus detected depending on whether or not the beam of light passes through the notch to be received by the light-receiving device. The method further comprises the step of determining the center axis line of the surface of the substrate in accordance with the position of the notch and the center of the surface. The method still further comprises the step of determining a measurement position on the surface of the substrate in accordance with the center axis line and measures the thickness of the electrically conductive thin film at the measurement position.
The film-thickness measurement method according to the present invention further comprises the steps of disposing a measurement coil in close proximity to the substrate and applying an AC voltage to the measurement coil to generate an eddy current in the electrically conductive thin film on the surface of the substrate. The method further comprises the step of detecting a signal produced in the measurement coil by an effect of the eddy current to determine the thickness of the electrically conductive thin film in accordance with the signal.
The film-thickness measurement method according to the present invention further comprises the step of preparing a Maxwell""s inductance bridge by connecting a serially-connected circuit of two reference resistors in parallel to a serially-connected circuit of a measurement coil and a reference coil. The serially-connected circuit of two reference resistors has two reference resistors connected in series to each other; and the reference coil connected in series to the measurement coil is disposed at a position farther away from the substrate than the measurement coil. The method further comprises the step of using the Maxwell""s inductance bridge to determine a variation in inductance component of the measurement coil, and thereby detect a signal produced in the measurement coil.
The axis determination apparatus according to the present invention comprises the support mount, the drive mechanism for rotating the support mount, the light-emitting device disposed near the circumferential portion of the support mount, and the light-receiving device disposed opposite to the light-emitting device to interpose the surface including the surface of the support mount therebetween. With the circular substrate having the notch formed on the circumferential portion thereof being supported on the support mount, the light-receiving device receives the beam of light emitted from the light-emitting device when the notch of said circular substrate stays in between the light-emitting device and the light-receiving device.
With this configuration, rotating the support mount to rotate the substrate allows the light-receiving device to receive the beam of light emitted from the light-emitting device only when the notch formed on the circumferential portion stays in between the light-emitting device and the light-receiving device. This makes it possible to detect the position of the notch by means of the light-emitting device and the light-receiving device.
Since the notch is formed on the circumferential portion of the substrate, the position of the center of the substrate is determined in advance, and the position of the center of the substrate is connected to the position of the notch detected, thereby making it possible to determine the center axis line of the substrate surface.
Incidentally, the axis determination apparatus according to the present invention may comprise a lifter having a support member and a projected member provided on the support member. The support member is provided with a gradually inclined surface sloped towards the projected member; and the projected member is adapted to place the circumferential portion of the substrate thereon. The axis determination apparatus may be adapted such that the virtual center of the lifter overlaps the center of the support mount upon placing the substrate onto the support mount from the lifer.
When the substrate is placed on the lifter, this configuration allows the substrate to fit into the projected members along the gradually inclined surfaces. The substrate then sits at the predetermined position of the lifter with the circumferential portion of the substrate staying on the projected member, and the substrate is thus supported on the lifter with the center of the substrate in alignment with the virtual center of the lifter.
In this case, the virtual center of the lifter is allowed to overlap the center of the support mount upon placing the substrate onto the support mount from the lifter, thereby causing the center of the substrate to be aligned with the center of the support mount. Accordingly, the lifter makes it possible to know the position of the center of the substrate.
The film-thickness measurement apparatus according to the present invention comprises the axis determination apparatus of the present invention and the measurement apparatus adapted to measure the thickness of an electrically conductive thin film formed on a surface of a circular substrate. The measurement apparatus is designed to move over the surface of the substrate in accordance with the center axis line determined by the axis determination apparatus.
With the center axis line of the substrate surface determined by the axis determination apparatus, this configuration makes it possible to employ the center axis line as the coordinate axis to set coordinates on the substrate surface, thereby allowing for knowing predetermined measurement positions on the substrate surface. This makes it possible to determine the thickness of the thin film at a plurality of measurement positions, thereby determining the thickness distribution of the thin film.
Incidentally, the film-thickness measurement apparatus according to the present invention may comprise the measurement apparatus including the film-thickness sensor, the power source, and a measurement device. The film-thickness sensor comprises the measurement coil. The power source is adapted to apply an AC voltage to the measurement coil when the substrate is in close proximity to the measurement coil to generate an eddy current in the electrically conductive thin film on the substrate surface. The measurement device may be adapted to measure a signal produced by an effect of the eddy current in the measurement coil.
In the measurement apparatus configured as described above, the measurement coil provided in the film-thickness sensor is arranged in close proximity to the substrate. In this arrangement, an AC voltage is applied to the measurement coil to generate an eddy current in the substrate to determine a signal, produced in the measurement coil by an effect of the eddy current generated in the substrate (such as, the amount of variation in inductance component). This makes it possible to determine the thickness of the thin film deposited on the substrate surface.
The amount of variation in inductance component of the measurement coil is determined by means of a highly sensitive measurement circuit using an inductance bridge.
FIG. 5 is an explanatory block diagram illustrating the principle for measuring inductance components according to the present invention, with a Maxwell""s inductance bridge designated by reference numeral 30.
The inductance bridge 30 comprises two serially-connected reference resistors 34, 35, which are connected in parallel to a reference coil 32 and a measurement coil 31 that are connected in series to each other.
With the inductance bridge 30 kept in balance, no voltage appears between output terminals 43 and 44 of the inductance bridge 30 even when an AC voltage VD is applied to the inductance bridge 30 by an AC voltage source 36 connected between the input terminals 41, 42 of the inductance bridge 30.
With the inductance bridge 30 kept in balance, bringing a substrate 50 close to the measurement coil 31 causes an eddy current to be generated in the substrate 50, resulting in a variation in inductance of the measurement coil 31. This variation drives the inductance bridge 30 out of balance, causing a voltage VS to appear between the output terminals 43, 44.
Suppose that an AC voltage VD to be applied to the inductance bridge 30 is expressed as shown below. That is,
VD=VD0xc2x7exp(ixcfx89t). 
Then, a voltage VS appearing between the output terminals 43, 44 is given by                               V          S                =                  xe2x80x83                ⁢                              V            S0                    ·                      exp            ⁡                          (                                                ⅈ                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                  t                                +                φ                            )                                                              =                  xe2x80x83                ⁢                                            V              S0                        ·                          exp              ⁡                              (                                  ⅈ                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                  t                                )                                      ·                          cos              ⁡                              (                φ                )                                              +                                    ⅈ              ·                              V                S0                            ·              exp                        ⁢                                          (                                  ⅈ                  ⁢                                      xe2x80x83                                    ⁢                  ω                  ⁢                                      xe2x80x83                                    ⁢                  t                                )                            ·                                                sin                  ⁡                                      (                    φ                    )                                                  .                                                        
A component of the voltage VS in phase with the input voltage VD and another component 90 degrees out of phase therewith are measured, and a variation in magnitude of the inner circumference of the measurement coil 31 can be determined in accordance with the ratio of the two components.
The amount of variation in inductance component is indicative of the eddy current loss in the substrate 50. Since the frequency of the AC voltage VD is known, the thickness of a thin metal film formed on the surface of the substrate 50 can be determined if the specific resistance of the substrate 50 and the thin metal film are known.
FIG. 8 is a graph showing an example of the relationship between the amount of variation in inductance component and the thickness of a thin copper film formed on a substrate surface. The AC signal applied has a frequency of 2 MHz and the AC voltage VD has a magnitude of several volts.
Since the amount of variation in inductance component of the measurement coil 31 varies depending on the thickness of the thin copper film formed on the surface of the substrate as can be seen from the graph, the relationship between the amount of variation in inductance component and the film thickness is measured in advance. The amount of variation in inductance component is measured in the absence of the substrate or the substrate having no thin film formed thereon brought close to the measurement coil. Subsequently, a thin copper film is formed on the surface of the substrate and the substrate having the film deposited thereon is then brought close to the measurement coil to determine the amount of variation in inductance component of the measurement coil. Consequently, the thickness of the thin film deposited can be determined in accordance with the determined amount of variation in inductance component.
As described above, according to the film-thickness measurement method of the present invention, the measurement coil is brought into close proximity to the substrate to generate an eddy current in the electrically conductive thin film formed on the substrate surface. The thickness of the electrically conductive thin film is then determined in accordance with the amount of variation, caused by this eddy current, in inductance component of the measurement coil. This makes it possible to determine the actual thickness of the film with accuracy. In addition, the determination of the thickness of the thin film by measuring the amount of variation in inductance component makes it possible to determine the film thickness at a predetermined position in a very short time.
Furthermore, the deposition apparatus according to the present invention comprises deposition means and the film-thickness measurement apparatus of the present invention. This makes it possible to measure the thickness of the thin film deposited and thereby determine the film-thickness distribution without taking the substrate out of the deposition apparatus.
The axis determination method according to the present invention allows the center of the substrate to be detected, and then the position of a notch provided on the circumferential portion of the substrate to be then detected. This makes it possible to determine the center axis line of the substrate surface by connecting the position of the notch to the position of the center of the substrate.
According to the film-thickness measurement method of the present invention, the center axis line is determined prior to the measurement of the film thickness. This procedure makes it possible to know the predetermined position on the substrate surface in accordance with the center axis line of the substrate. For example, both end portions of the surface of the substrate or a predetermined point on the surface of the substrate (such as, the position of the center) can be determined in accordance with the center axis line. This makes it possible to determine the thickness of the thin film at the predetermined points.